Prevention of silver occulsion in color photography



United States Patent 5 Claims ABSTRACT OF THE DISCLOSURE Prevention of silver occlusion in the bleaching and fixing for color development of photographic silver halide emulsions containing hydrophilic color formers including solubilizing groups, by incorporating in the emulsion prior to coating on a film base poly-N-vinyl-S-methyl-Z- oxazolidinone having a Sikentscher K value of about to 50.

This application is a continuation of Ser. No. 337,528 filed Jan. 14, 1964, now abandoned.

The present invention relates, in general, to photography and in particular to color photographic processes wherein objectionable silver occlusion is minimized or substantially prevented. More specifically, the present invention resides in provisions for the alleviation of the problem of silver occlusion in hydrophilic color photography systems.

Heretofore, according to customary practices, the problem of silver occlusion in hydrophilic color photographic systems has presented serious problems due to the fact that certain types of silver specks, which are often called passive, cannot be bleached from a color photographic image by normal means. When these passive silver specks remain after processing, they cause a degradation of the final color image. It is very likely that the type of color former used, and a great variety of color formers fall into this category, plays a major role in the formation of occluded silver which eventually is observed as these passive specks.

Many attempts or proposals have heretofore been suggested or attempted to prevent silver occlusion or, after it has occurred, to remove the occluded silver, but generally, these attempts have not been entirely successful. Among the attempts or proposals which have heretofore been suggested or recommended include those whereby the prevention of silver occlusion is accomplished by treatment of the emulsion prior to its application to the film or paper base. Alternatively, proposals or attempts for the prevention of silver occlusion have been suggested which concern modifying the developer with various additives. In addition, attempts have been made to remove the occluded silver with reactants or solvent or by mechanical means, after occlusion has occurred, but as pointed out above, many of these previous proposals have not been entirely satisfactory.

Accordingly, it is the primary object of this invention to prevent silver occlusion which normally occurs in the development of gelatin silver halide emulsions which contain hydrophilic color formers.

Other objects will be apparent from the following description.

As presently indicated, the present invention is predicated upon the discovery that silver occlusion in developed color photographic systems employing hydrophilic color formers can be eliminated by adding to the liquid silver halide emulsion, which contains the color former prior to coating upon a support, a homopolymer of N-vinyl-S- methyl-2-oxazolidinone characterized by the general formula:

CHaCH-O N Jill-CH2- wherein it corresponds to a degree of polymerization which provides a polymer having a Sikentscher K value of from about 10 to about 50, and represents a number ranging from 400 to 2000.

The Sikentscher K value is an art recognized and an accepted indication of relative molecular weights of polymers and is more fully described in the publication of H. Sikentscher Cellulosechemie 13, 58 (1932). In determining the K value the following formula is employed:

Log 1; rel.

where the relative viscosity (1; rel.) is measured for a 1% solution of the poly-N-vinyl-5-methyl-2-oxazolidinone (1 gram per ml.). 1

While not wishing to be bound by any particular mechanism or theory underlying the results obtained in accordance with the present invention, it is believed that the improvement is due, in all likelihood, to the ability of the aforementioned polymer to complex, in some manner, with hydrophilic color formers containing solubilizing groups of the group consisting of hydroxyl, carboxyl and sulfonic acid groups.

The homopolymers of the above-described class are ordinarily obtainable in the form of free-flowing white powders. They are readily soluble in acids such as glacial acetic acid, hydrochloric acid, and the like. In addition, they are somewhat soluble in warm water, essentially insoluble in the lower alcohols, particularly methanol and are essentially insoluble in amines and amides. While they are less soluble in the aliphatic alcohols, they are soluble in chloroform, methylene chloride, and acetone. By appropriate choice of an appropriate solvent compatible with the hydrophilic color former, the homopolymer may readily be incorporated into the emulsion system.

The proportions of the homopolymer which are added to a solution or emulsion of color formers to achieve the desired results are not necessarily a critical feature of the invention and can be varied somewhat, depending upon the particular color former employed and the other components of the composition employing the same. In general, amounts of homopolymer of from 0.01 to .4 gram per 50 grams of emulsion or one gram of color former are normally preferred, although amounts somewhat above or below the above-described range can be employed if desired.

The photographic color formers which find utility in the practice of the invention include the hydrophilic color formers of the cyan, yellow and magenta types. These color formers are fast to diffusion and contain a solubilizing carboxy or sulfo group, and react with the oxidation products of a primary aromatic amino developing agent to azomethine, indoaniline or phenazonium dyes. Representative hydrophilic color formers which are suitable for use in practicing the present invention are described and set forth in U.S. Patent Nos. 2,186,849; 2,186,851; 2,265,221; 2,829,975; 2,902,366 and include the following color formers by way of example: l-stearoylamino 4 (1' hydroxy 2 naphthoylamino) 3- sulfonic acid; l-phenyl-3-(3'-a-sulfostearamido)-benzamido-S-pyrazolone; and the like.

The poly-N-vinyl-5-methyl-2-oxazolidinone can be conveniently prepared by conventional polymerization tech- In carrying out the invention, the poly-N-vinyl-S- methyl-Z-oxazolidinone can simply be added to the color former solution before coating on a film base support.

The support which can be employed in carrying out the invention is of the conventional type, including the cellulose derivatives, for example, cellulose nitrate, cellulose acetate and other lower fatty acid esters of cellulose, as cellulose propionate, cellulose butyrate, cellulose acetate-propionate, cellulose acetate-butyrate and the like. Other supports, such as glass, paper, as well as polystyrene, polycarbonate and polyethylene terephthalate films can be used instead.

The following examples will serve to illustrate the practice of the invention, it being understood, that the examples must not be considered as limiting the scope of the invention.

EXAMPLE I Three samples of a silver halide emulsion having a weight of 25 grams each and each containing 0.5 gram of a color former of the formula:

were coated in the customary manner on a white opaque film base, which served as the support. Two of the coatings contained poly-N-vinyl-S-methyl-Z-oxazolidinone in the amounts shown below.

Coating No. Amount, grams 1 2 .1 3 .2

After identical exposures and reversal processing in the manner described in U.S. Patent 2,553,498 the coatings were visually inspected. Coating No. 1 showed the effects of silver occlusion as evidenced by a brownish-black appearance. Coating Nos. 2 and 3 were free of this defect and displayed a pure and brilliant yellow color.

EXAMPLE II Example I was repeated with the exception that five samples of a silver halide emulsion were used, each of which contained 0.5 gram of a color former of the formula:

were coated on a clear film base. Four of the coatings 4 contained poly-N-vinyl-5-methy1-2-oxazolidinone in the amounts indicated below:

Coating No. Amount, grams 1 0 After identical exposures and reversal processing the coatings were inspected. Coating No. 1 showed clear evidence of silver occlusion whereas coatings Nos. 2 to 5 were free of this defect.

EXAMPLE III Example I was repeated to the extent that five samples of a silver halide emulsion were used, which contained a color former of the formula:

The emulsions were coated in the usual manner on a white opaque film base which served as the support. Four of the coatings contained poly-N-vinyl-5-methyl-2-oxazolidinone as indicated below:

Coating No. Amount, grams 1 0 2 0.05 3 0.1 4 0.15 5 0.2

After identical exposures and reversal processing the coatings were inspected. Coating No. 1 showed clear evidence of silver occlusion, whereas coating Nos. 2 to 5 showed none.

Various modifications of the invention will occur to those skilled in the art as variations in the selection of emulsions, hydrophilic color formers and supports can be made without departing from the spirit and scope of the invention.

I claim:

1. A process for the prevention of silver occlusion in the production of a color photographic image by reversal development comprising incorporating, prior to coating on a support, in a silver halide emulsion containing a hydrophilic color coupler fast to diffusion, a homopolymer of N-vinyl-5methyl-2-oxazolidinone.

2. A process as defined in claim 1, wherein said homopolymer has a Sikentscher K value from 10 to 50, the number of monomer units therein ranging from 400 to 2,000.

3. A process as defined in claim 2 wherein said color former has the formula:

I -012 17 CH 4. A process as defined in claim 2 wherein said color former has the formula:

5. A process as defined in claim 2 wherein said former has the formula:

COOH

color 6 References Cited UNITED STATES PATENTS I. TRAVIS BROWN, Primary Examiner.

US. Cl. X.R.

Disclaimer 3,421,896.Alex P. Altavilla, Johnson City, NY. PREVENTION OF SILVER OCCLUSION IN COLOR PHOTOGRAPHY. Patent dated Jan. 14,

1969. Disclaimer filed Sept. 30, 1982, by the assignee, Eastman Kodak Co.

Hereby enters this disclaimer to all claims of said patent. [Ofiicial Gazette March I, 1983.] 

